This invention relates to vehicle steering alignment and, more particularly, to a method and apparatus for aligning the wheels or wheel hubs of a vehicle during assembly on a moving assembly line for attachment of the vehicle steering wheel in a straight ahead position while the vehicle wheels remain in substantially parallel alignment.
It is known in the art relating to automotive vehicles to provide methods and apparatus for aligning the steerable front wheels of a vehicle with respect to the frame or other reference structure in accordance with predetermined alignment parameters. Such alignment procedures are usually carried out with the vehicle in a stationary position and with the associated steering wheel of the vehicle set in the straight ahead position. In some cases, means are provided for adjusting the rotational position of the steering wheel relative to the associated steering linkage when the steerable front wheels of the vehicle are aligned in the straight ahead position.
In connection with the planned assembly of a new vehicle, it was desired to eliminate any means for adjusting the steering wheel relative to the steering linkage after assembly of the wheel to the linkage. Thus, in order to assemble the steering wheel in the straight ahead position on the linkage, it would be necessary to first align the vehicle wheels in a straight ahead position and then attach the steering wheel to the steering linkage with the wheel in the straight ahead position. An efficient method and means for accomplishing the desired results was thus required.
The present invention provides an apparatus and method for accomplishing the desired purposes of aligning the front wheels of a vehicle to a straight ahead position substantially parallel with the rear wheels so that the steering wheel may be attached to the steering linkage with both the steering wheel and the steerable front wheels in their straight ahead positions. The apparatus and method developed for this purpose provide for alignment of the steerable wheels and attachment of the steering wheel while the vehicle structure is being assembled on a moving assembly line.
Terms such as xe2x80x9csubstantially parallelxe2x80x9d and xe2x80x9csubstantially longitudinally parallelxe2x80x9d as used in the specification and claims are intended to include not only exactly parallel alignment of vehicle wheels in a straight ahead position but also adjustments of the steerable wheels to provide toe-in or other adjustments such as caster and camber which may result in slightly non-parallel alignment of the vehicle wheels in the straight ahead position.
An apparatus according to the invention includes a tool rail or track running parallel and to one side of the centerline of a conveyor on which the partially assembled vehicle chassis is carried. Two sets of laser devices or boxes are carried on the tool rail. One of the laser devices aligns with one of the wheel hubs on a rear axle and the other aligns with a front wheel hub on the same side of the vehicle. Each of the laser devices includes a pair of laser heads which align with longitudinally spaced opposite sides of a machined surface of an associated hub. The laser heads are connected with known laser scanning equipment to indicate the relative longitudinal angle of the plane of the hub surface with respect to the tool rail and therefor with respect to the centerline of the conveyor on which the chassis is carried.
In the apparatus as developed, the rear wheel alignment box or laser device is fixed longitudinally but adjusts vertically for alignment with the rear axle of each vehicle as it passes by the laser device on the assembly line. In contrast, the front wheel alignment box or laser device is mounted to move vertically along the tool rail for a predetermined distance, as well as to move vertically as needed for alignment with the steerable front wheel hub of the vehicle. In this way, the laser device is able to continuously monitor the angular position of the front hub as the chassis moves along the line for the selected distance. The distance is made long enough to normally accomplish alignment of the steerable front wheels of the vehicle during the period of motion of the chassis over the selected distance.
The operating system for the front laser device or alignment box is programmed to coact with a power wrench mountable by an operator to a portion of the steering linkage of the vehicle, such as the steering gear or the end of the steering shaft, prior to assembly of the steering wheel. The front axle laser head. readings fed to a computer indicate the relative longitudinal angular position of the front wheel hub. The system then initiates operation of the power wrench to turn the steering linkage in the proper direction to move the steerable front wheel hubs to the same or substantially the same angle relative to the centerline of the conveyor as the angle of the rear wheel hub has with the centerline of the conveyor as measured by the rear laser heads.
When the relative angles of the front and rear hubs are equal or at a predetermined setting substantially equal, the power wrench operation is concluded and the wrench is removed from the assembly by the operator. At this point, the planes defined by the sensed machined surfaces of the two wheel hubs on the same side of the vehicle are positioned parallel or substantially parallel to one another so that the wheels are aligned in longitudinally substantially parallel positions which result in straight ahead motion of the vehicle in subsequent operation, Thus the wheels are aligned in the straight ahead position. At this point, the steering wheel for the vehicle may be assembled to the steering shaft with the wheel position in the desired straight ahead position so that the final assembly is aligned with the steering wheel and front wheels both in the desired straight ahead position at the time of vehicle assembly.
In accordance with the invention, a method of operation of a particular embodiment of alignment apparatus is as follows:
First, a laser triggers the front wheel alignment box to track the speed of the assembly line.
While tracking the front wheel hub, the trigger laser is servo-driven up to find the top of the target front wheel hub. The two longitudinally spaced alignment laser heads are then servo-driven outward to find the leading and trailing edges of the machined surface which is the target measuring surface for the lasers.
Correct height and width information is sent to the rear wheel alignment box which causes the rear alignment box to move to the correct height and then wait for the passage of the rear wheel hub.
When both rear wheel hub lasers are positioned on the target, an instant measurement of the wheel angle is taken and stored in a computer.
The system then signals the operator to start correcting the front wheels. A power wrench will automatically turn clockwise or counterclockwise depending on the angle of the front wheel measurement relative to the rear wheel hub measurement angle.
The power wrench is shut off when both wheel angles match so that the wheel hubs are aligned with their planes parallel or substantially so. A signal is then given to the operator to remove the power wrench.
The front wheel alignment box returns to its starting position and waits for the next chassis.
The offset angle is archived by the computer.
An overtravel limit will stop all motion and operation if the front wheels are not aligned in the given travel length of the front laser head. A homing routine will reset the system.
An exemplary system in accordance with the invention includes the following elements:
A fixed alignment box for the rear wheel hub.
A moving alignment box for the front wheel hub.
A control panel with programmable computer (PC) and motion controller.
A fifty foot rail system to carry the front wheel alignment box.
Interface and motion control software programming for controlling the system in accordance with the previously outlined method.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.